Research and development of HEB mixers for terahertz heterodyne receivers in atmospheric science

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Objective

This project is focused on the development of hot electron bolometric (HEB) mixers for airborne terahertz heterodyne receivers in atmospheric science. The key frequencies are 1.5THz, 2.5THz and 3.5THz where HBr and OH, two important molecules in stratospheric chemistry, have rotational transitions. The objectives are to develop and characterise HEB mixers for 1.5THz, 2.5THz and 3.5 THz. Different types of mixers and mixer mounts will be compared, especially diffusion cooled HEB mixer versus phonon-cooled HEB mixer and quasi-optical mixer versus waveguide mixer at 1.5THz and 2.5THz. The optimum mixer configuration for each frequency will be determined. A solid-state local oscillator based on a multiplied BWO will be developed and characterised for 1.5THz and 2.5THz. Finally the airborne THz heterodyne receiver operated by DLR will be modified in order to make use of the more sensitive HEB mixers than the so far used Schottky diode mixer and in order to implement the solid state local oscillator. In a field campaign the receiver will be tested aboard an airplane and atmospheric spectra will be measured and analysed.

The research activities to achieve this goal can be roughly divided into three phases: First basic research will be done on the phonon cooled and diffusion cooled HEB mixers in order to optimise the fabrication procedure, the reproducibility and the stability of the devices. The devices will be tested in different mixer mounts and at different frequencies in order to determine the optimum performance in terms of sensitivity, antenna pattern. Special emphasis will be put on the comparability of the results. Therefore different partners will perform the characterisation. In the second phase the subcomponents of the receiver such as the low-noise and wide band cryogenic amplifier, the room temperature IF chain, the quasi-optics and the backend will be developed. The most important subtask in this stage is the development of the solid-state local oscillator. In the third and final phase all subcomponents will be integrated into the modified DLR airborne heterodyne receiver, which will be airborne certified. In a field campaign the receiver will be tested and atmospheric emission spectra of OH and HBr will be measured and analysed.The major expected results are: optimised HEB mixers in the frequency range from 1.5THz to 3.5THz, solid state local oscillators for 1.5THz and 2.5THz, an airborne heterodyne receiver for HBr and OH and atmospheric data on OH and HBr. Apart from the applications this project has in atmospheric science there will be a major impact on the development of heterodyne receivers for other airborne and space borne applications such as SOFIA or FIRST.